1. Field of the Invention
This invention relates to a method for preparing a flame retardant modified acrylonitrile-based copolymer and a flame retardant fibrous material comprising the flame retardant modified acrylonitrile-based copolymer.
2. Description of the Related Art
Acrylic fiber is made from polyacrylonitrile, and has excellent chemical and physical properties, such as dyeing affinity, tactile feeling, and light resistance. However, it has poor flame retardance, which restricts its use for production of anti-flammable textile products, such as anti-flammable curtains, carpets, and clothes.
It has been found that acrylonitrile-based copolymer, which maintains the excellent chemical and physical properties of polyacrylonitrile, is a better candidate for making anti-flammable textiles.
In order to improve the flame retardance of acrylonitrile-based copolymer, several methods have been proposed to modify the acrylonitrile-based copolymer, such as addition of a halogen-containing monomer (which provides a flame retardant function), such as vinylidene chloride, and/or addition of flame retardant agents into a reaction system to form the modified acrylonitrile-based copolymer. Conventionally, the reaction system contains 20 wt % to 50 wt % of vinylidene chloride. However, addition of the halogen-containing monomer in such an amount in the reaction system complicates the copolymerization reaction, and results in a considerable reduction in the polymerization degree of the modified acrylonitrile-based copolymer.